The Summer of HEAT and HUMIDITY - Passive House Comfort Performance

The Summer of HEAT and HUMIDITY
Passive House Comfort Performance

CAUTION: THERE IS SOME VERY TECHNICAL DATA HERE.

If you understand things like Psychrometric Charts, Enthalpy, ASHRAE 55 (comfort criteria), and Indoor Air Quality Metrics, you may like this post.


It has been a while since I did a blog post that didn't have to do with an open house, so I am going to be a little rusty - and buckle in, it is a long one!

As everyone knows, this has been a very warm summer, and we have been dealing with some very humid conditions as well. I thought that this would be a good opportunity to see how Rochester Passive House performs to the standards for comfort. You can also be the judge if you'd be comfortable.

The purpose of this post is to show how effective the "minisplit per floor" method of cooling is in a Certified Passive House AND to show how we maintained superb Indoor Air Quality despite Poor Air Quality warnings from the local weather stations. Here is the set up:

1) 9000 BTU Ductless minisplit is located in the Master Bedroom on the south end of the house

2) uHoo IAQ Meter in kids bedroom on North Side of the house.

3) Netatmo Weather Station located on the front porch out of the direct sunlight

I put the uHoo IAQ meter in the kids bedroom for a few reasons

1) I have 2 girls - age 8 and 6 who share a room (2 occupants = higher potential CO2)

2) This room on the north east side of the house on the 2nd floor seemed to me be to be the most difficult to cool

3) I care about the IAQ for my kids, so I wanted to see if there was a problem in their room

4) They have a pretty routine bedtime and wake up time every day, so I figured my numbers would be consistent between the days. (8pm bedtime, 7am wake up - YES EVEN IN THE SUMMER)

Now, our method for cooling with the minisplits were:

1) We kept the master bedroom door open every day and all night

2) We closed the kids door every night - they did open it a few times to go to the bathroom etc, and left it open. 

3) We did do laundry at our normal rate, about 5 loads per week with a condensing dryer

4) Our Zehnder system was on "normal" except for times of boosting (showers and cooking)

5) The minisplit in the Master Bedroom was kept on "dehumidify" I figure it is trying to maintain 60% RH regardless of temperature. I can't find a good explanation on this anywhere.

6) Our 1st Floor minisplit was either set at 72F or Dehumidify - we change it around for comfort

Just How Hot Was it?

The typical HVAC design criteria for Rochester, New York is set for 1% and 99%. This means the outdoor temperature will only exceed the design temperature 1% of the hours of the year.  

Rochester NY Cooling Design Temperatures - from ACCA Manual J are:

1% Cooling - 86 F 50% RH

Because I will be discussing Temperature AND Humidity we will convert things to Enthalpy for comparisons. Simply put, the higher the Enthalpy, the higher the total heat content in the air. 

86 F with 50% RH has and Enthalpy of 35.3 BTU/lb

What does this look like on a Psycrometric Chart?

Okay, lets take a look at the outdoor weather from 9am June 28th - 7am July 6th

This is a mapping of temperature and humidity readings every hour for that 8 day period 

There are 191 measurements.

Of the 191 hours in this time period the Enthalpy for design was exceeded for 115 hours!

(There are 115 red dots above the red line)

I am not making an argument for or against the design limits set by ACCA, I am simply showing how hot it was over this week. 

60% of the time we were exceeding the design temperature limits for our cooling system.

--------------------------------------------------------------------------------------------------------------------------

Lets Define Comfort

ASHRAE-55

"The purpose of this standard is to specify the combinations of indoor thermal environmental factors and personal factors that will produce thermal environmental conditions acceptable to a majority of the occupants within the space"

That is a lot to digest, so lets unpack that a little bit:
1) Thermal Environmental Factors - things like temperature, mean radiant temperature and humidity etc.
2) Personal Factors - things like the amount of clothing you are wearing, your activity levels etc.
3) A majority of the occupants - lets face it, we can't make EVERYONE happy, some people like it warm, others like it cool.

There are a few different models you can use to meet this standard -
1) Graphic Comfort Zone Model - to use this model you must meet the following criteria:

• metabolic rate must be between 1.0-1.3 - For intermittent activity, you take the average
• 0.7 - sleeping
• 1.0 - seated and quiet
• 1.2-1.4 - light activity
• 2.0 - walking, lifting heavy loads
• Anything higher has a low level of design accuracy
• Humidity ratio must be below 0.012 lb H2O/lb dry air
• that is 84 grains H2O per lb dry air

2) Analytical Comfort Zone Model - If either or both of your above criteria are too high, you use this method.

• Utilized this comfort tool model with inputs of:
• Operative Temperature (or Air Temperature and Mean Radiant Temperature)
• Air Speed
• Humidity
• Metabolic Rate
• Clothing Insulation
• These inputs are evaluated to predict a thermal sensation on a -3 (cold) to +3 (hot) scale
• You comply if the conditions show thermal "neutrality" between -0.5 and +0.5

Okay! WAKE UP! Moving On....

EN-15215 

This is the European Standard for comfort. 

For what I am trying to show within a Certified Passive House, EN-15251 and ASHRAE-55 are pretty similar. Since there is no temperature asymmetry and I am utilizing the residential standard for comfort (ie: we are not designing to maintain an exact temperature and humidity, like we would in a museum or hospital) the 2 standards are close enough without writing a book. 

I am simply trying to show how well we achieved summer comfort when the outdoor conditions exceeded our design conditions for an extended period of time.

--------------------------------------------------------------------------------------------------------------------------

Comfort Criteria Assumptions:

• I will utilize the Analytical Comfort Zone Model via http://comfort.cbe.berkeley.edu/
• When the Kids are "sleeping" the MET will be 0.7 - 8pm-7am
• When the Kids are awake and during the day the MET will be 1.0
• The room is typically unoccupied during the day, but I have the data so lets look at it
• The Clothing Level (Clo) at night will be 2.0
• Kids in summer PJ's under a blanket on top of a mattress
• The Clothing Level (Clo) during the day will be 1.0
• The house is airtight, there is no ceiling fan and the way the ventilation system is designed there is no noticeable air velocity in the room. The Standard seems to have a 30 Feet Per Minute default, so we'll go with that (30 feet per minute = 0.34 miles per hour)
• The Mean Radiant Temperature is 77 F. This is a guess and tends to be the standard default. but there are no computers, electronics or other internal gains in the room other than the 2 girls. One alarm clock is the only thing plugged in. There is also 1 Passive House Window that faces east, so by 11 am it is completely shaded. The walls, floor and ceiling temperatures were measured with an IR Camera showing about 75.2 F

Kids Room Nighttime Comfort

So what does this mean?

• There were 96 hours where the kids were in their room "sleeping" over this time period
• The Average Predicted Mean Vote or PMV needs to be between 0.5 and -0.5. In this model the Average PMV is -0.06 - Thermal Comfort is achieved.
• The conditions in the bedroom stayed within the comfort zone (indicated by the light purple shading) the entire time.

Kids Room Daytime Comfort

• There were 95 hours during the day 
• The Average Predicted Mean Vote or PMV needs to be between 0.5 and -0.5. In this model the Average PMV is +0.07 - Thermal Comfort is achieved.
• The conditions in the bedroom stayed within the comfort zone (indicated by the light purple shading) the entire time.

You will notice a slight shift in the light purple comfort zone, due to different met rates and clothing levels. 

--------------------------------------------------------------------------------------------------------------------------

So that is great, Thermal Comfort is achieved even when the temperatures are extreme for a long period of time. All without conditioned air distribution. But what about the indoor air quality?

The uHoo meter is measuring and data logging lots of air quality conditions every minute of every day. It also has tapped into the EPA's recommendations on limits for exposure on each. I get a notification when any one of these items exceeds the EPA's limits.

• Temperature -        Notification at 77 F
• Humidity -              Notification at 60 % (or below 35%)
• CO2 -                       Notification from 1000-5000 ppm - Warning over 5000 ppm
• Total VOC -            Notification from 400-800 ppb - Warning over 800 ppb
• PM2.5 -                   Notification from 50-100 ug/m3 - Warning over 100 ug/m3
• NO2 -                       Notification from 100-250 ppb - Warning over 250 ppb
• CO -                        Notification from 35-70 ppm - Warning over 70 ppb
• O3 -                          Notification from 55-70 ppb - Warning over 70 ppb
• Air Pressure -         Below 970 mbar or above 1030 mbar indicating a sever weather event

To save time and effort, I will omit the following readings since they didn't change the entire week:

Temperature and Humidity - I don't need to beat a dead horse

Carbon Monoxide = 0 ppm all the time

Air Pressure = 986.5-1003.6 mbar all the time

New York State Measures a variety of Outdoor Air Quality Metrics available to anyone at any time. Here is the Website link:
http://www.nyaqinow.net/

The Nearest Station to me is roughly 13 miles away.

Lets take a look at PM 2.5 measurements

PM2.5 is "Particulate Matter" that are 2.5 microns or less in width. That is a fancy way of saying "tiny dust". PM 2.5 is small enough that the body cannot filter them out when inhaled and thus enter our lungs and get absorbed into our blood.
According to the EPA you want to maintain between 0 - 50 ug/m3

My kids room vs. Ambient for the same time period:

The Blue Line is Outdoor Measurements from the NYS website.
The Orange Line is Indoor Measurements from the uHoo Device.

Over this time period:
the Outdoor Average PM 2.5 was: 10.8
 the Indoor Average PM 2.5 was: 6.1 (and never exceeded 8.1)

Lets take a look at NO2 Measurements

NO2 forms from ground level emissions related to burning fossil fuels from vehicles, power plants,
and off road equipment. According to the EPA scientific evidence links short-term NO2 exposure, ranging from 30 minutes to 24 hours, with adverse respiratory effects including airways inflammation in healthy people and increased respiratory symptoms in people with asthma. You want to stay under 100 ppb

The Blue Line is Outdoor Measurements from the NYS website.
The Orange Line is Indoor Measurements from the uHoo Device.

Over this time period:
the Outdoor Average NO2 was: 4.3
 the Indoor Average NO2 was: 0.5 (and never exceeded 0.6)

Lets take a look at Ozone (O3) Measurements

Ozone is not directly emitted into the air, but is created by chemical reactions between oxides of nitrogen (NOx) and Volatile Organic Compounds (VOC's) in the presence of sunlight. Breathing ozone can trigger a variety of health problems, particularly for children, the elderly and people with lung disease and asthma. You want to maintain levels as low as possible because breathing low levels over a long period of time may have more damaging and longer-lasting effects.
The safe level according to the EPA is under 55 ppb, however inhaling fairly low levels can still result in signs and symptoms such as coughing, congestion, etc.

The Blue Line is Outdoor Measurements from the NYS website.
The Orange Line is Indoor Measurements from the uHoo Device.

Over this time period:
the Outdoor Average O3 was: 38.6 ppb
 the Indoor Average O3 was: 4.0 (and never exceeded 4.4)

DISCLAIMER: Ambient Total VOC and CO2 are not currently measured by NYS.
I don't have data to the compare the indoor conditions to. I have moved the uHoo devide outside, and I taking some measurements to see how CO2 and TVOC (and all of the other measurements for that matter) varies. That data will be posted when I see something interesting.

Lets take a look at Total VOC Measurements

VOC's are carbon based chemicals that are emitted as gases from solids or liquids. While most people can smell high levels of some VOC's, others have no odor. There are thousands of different VOC's produced in our every day lives (Paint, Cleaning Solutions, Wood Products, Cooking, Air Fresheners,etc. etc.). The EPA recommends adding ventilation when above 400 ppb, and avoiding concentrations over 800 ppb.

The Orange Line is Indoor Measurements from the uHoo Device.

Over this time period:
 the Indoor Average TVOC was: 64.5
The 400 ppb limit was exceeded for 2 hours with a max reading of 471.9.

There is no direct correlation between an outdoor measured condition and the indoor condition for TVOC. I have been reading TVOC measurement outdoors as of late and have seen readings as high has 317 ppb, so it is plausible the indoor VOC spike was caused from an outdoor concentration spike.

Lets take a look at CO2 Measurements
CO2 concentrations are generally related to the number of occupants. It is usually highest where people and pets spend most of thier time. Some other sources include, combustion appliances, and from experience - bread baking (and rising). CO2 is generally considered to be 400 ppm in outdoor air. The ideal state is under 1000 ppm in the house. Elevated levels can lead to drowsiness, but no serious health effects until you exceed 5000 ppm. Headaches, increased pulse rate, decrease in cognitive thinking etc. can result.

Our ventilation system is designed to maintain roughly 600-700 ppm CO2 in the house (or 200 ppm above ambient).

The Orange Line is Indoor Measurements from the uHoo Device.

Over this time period:
 the Indoor Average CO2 was: 795

The 1000 ppm limit was exceeded on 5 occasions.  There are a few reasons for this.

• Outdoor ambient CO2 was likly high. On recent warm muggy nights I have seen the outdoor CO2 creep up to as high 632 ppm. 
• Ventilation Rates not high enough with high ambient CO2. While the system is designed to keep the CO2 levels in the 600-700 ppm range, it does consider that our winters are longer and CO2 concentrations are lower in the winter. 
• Extremely warm and humid nighttime temperatures are difficult for any cooling / ventilation system. 

We have an interesting dilemma here. On the worst night for CO2 concentration, our low temperature was 75.8 F with a 86% RH. If we increase our ventilation rate to lower the CO2 concentration we jeopardize the indoor comfort levels due to excess humidity. We do have an ERV, but when it is used in conjunction with the Comfofond typically it runs in bypass. This is because the Comfofond is lowering the temperature of the incoming air below the temperature of the extract air (ie: "Free" Cooling). When it cools the incoming air with the ground loop, the fresh air is near the saturation temperature (meaning it is very humid, but cooler). Usually in the 65-70 F range. 

For more information on my ventilation system see my previous blog post HERE

Because the CO2 levels are only elevated for a few weeks out of the year; 
AND they are no where near the dangerous levels 
AND all of the other indoor air quality metrics are within limits 

We are certainly satisfying any concerns of comfort with a spot source cooling unit.  

Construction Update 2

Construction Update 2

Things have been happening at a fairly rapid pace for the past few weeks. 

• Both the plumbing and electric rough in's have been completed, and inspected. 
• Our electric meter was installed by the Utility.  
• Insulation of the outer wall assembly is complete
• The Zehnder Ventilation system has been installed (except for the ducting to the outside)
• The air source heat pumps have been installed.

Here are some Photos of us dense packing the outer wall assembly:

 The Mento WRB was slit in a knife, and our dense pack hose was fed into the cavity. 

The holes were then taped with the Vana Tape from 475 Supply.

Lets take a closer look at the plumbing system:

 We have incorporated a few different components not very common in our area. 

Drain Water Heat Exchanger

This is a slick little device. It looks like a big copper tube. From an engineering perspective, the fewer moving parts the better! Moving parts break or need maintenance. In a Passive House the largest energy load is heating hot water. The drain water heat recovery component simply takes the warm water going down the drain and "pre-heats" the cold water going to the shower valve as well as the cold water entering the water tank. The efficiency of this component is directly related to length. In our case, we are using a 48" long heat exchanger. This will recover roughly 50% of the heat going down the drain. 

Hot Water Circulating Loop

We decided to utilize a hot water recirculating pump for a few reasons. 

1) We have a raised fill septic system and with a recirc pump we will save thousands of gallons of water per year and put less stress on our septic system.

2) Hot water will be the largest single energy user in our house. When you open the hot tap, the ambient water leaves the tap and goes down the drain. The water heater tank then begins to feed the hot water into the system. The tank is then filled with cold water from the street. It is then heating that water from 50 degrees (or less) to the desired temperature. With a recirc we will just be reheating the ambient water in the loop (70 degrees or so). This is a huge savings in energy!

Check out how the system works here:

Both of these items require us to insulate the hot / tempered water pipes. The insulation will only make these systems work better.

Hose Bibs

Hose bibs are something I wish I had given more though earlier in the process. Probably the best thing would have been to do Yard Hydrants, since they exit the house underground, the thermal bridge impact is much less. The Rim Joist insulation is 24" deep. we decided to go with a 14" hose bib connected to Pex with a shutoff valve inside the basement. The Pex is much less conductive than the copper, but also ensures the hose bib copper shutoff should never get to the freezing point.

Rough Electric

Not much is different on the electric side of things. In an effort to minimize the electrical penetration to the outside we decided to install a sub panel in the Garage to power all of the exterior lighting. The only other electrical penetrations are from interior switches to exterior lights. Those holes were sealed using special wire gaskets from 475. This made air sealing the wires very fast and easy. There were no complaints from the electrician.

The only other difference is our options of "recessed lighting" on the 2nd floor. We have a 2" space for fixtures. With the advances of LED lighting technology, we have decided to utilize LED surface mount lights that look like recessed lights by fit into standard Junction Boxes

 These retail for about $25 each.

Whole House Ventilation

To ensure superb indoor air quality, the Zehnder HRV will ensure we have full exchange of all of the air in the house once every 3 hours with fresh filtered air. 

A standard room 2 tube register 

The 3" tubes are inserted to the register with a gasket

Each 3" tube is run separately back to the HRV

The tubes are then inserted back into the HRV with another gasket. 

The red tubes indicate the "extract air" which will remove the stale air from the kitchen and bathrooms. The blue tubes will supply the fresh filtered air to bedrooms and living spaces. I will go into more detail on this system before commissioning.

Ductless Minisplits

 We installed two 9000 BTU/hr Mitsubishi Mr. Slim heat pumps. I should note that only one is needed to meet the load requirements

This is the downstairs heat pump. It will basically be used for heating. It will probably only need to do some cooling when we have a large party.

 This is the upstairs heat pump. It will basically be used for cooling only. Since cold air drops, getting the air conditioned air upstairs can be challenging for such a low flow ventilation system. 

Stay tuned for another update soon as we will be holding an open house in the next week or so and finishing the insulation before drywall!

Construction Update 1

Construction Update #1

It has been a week or so since I did my last update. With regards to passive house details and different construction techniques, not much new has happened.

Basement waterproofing

In the Passive House world you hear the term "Belt and Suspenders". Basically double up on things to make sure you get the result you want. We used Mel-Rol; a water based liquid applied waterproofing membrane. Then we installed a prefabricated dimple membrane over that.

Finished grade will come to the top of the black membrane. Above that we will finish with a Conproco waterproofing product.

Basement Steel Delivery

We will have 4 posts in the basement that support 2 steel beams. The beams will only span from the front (West) side of the basement to the stairs along the back (East) wall. Remember we do have 8" of foam under the footer under the post.

Comfofond Heat Exchanger Tubing

When we had Zehnder design our whole house ventilation system we had them include the geothermal incoming air preheater. Basically, we will be pumping a brine through the tubing to a heat exchanger coil in the house and the incoming air will pass over it. This provides some tempering in both the summer and the winter.

In the summer the brine loop will "precool" the air before it reaches the air to air heat exchanger allowing the overall efficiency to increase and give us up to a half ton (6000 BTU/hr) of cooling.

In the winter the brine loop will "preheat" the air before it reaches the air to air heat exchanger allowing the overall efficiency to increase and keep the air entering the house within 3 degrees of extract air.

We will revisit the overall design of the system when we install the system later on.

According to Zehnder's design specs, based on our soil type, and system size we need roughly 200' of tubing 

Since the perimeter of our house is just under 160 feet - doing 2 full loops would be a little too long, so we went around 3 sides of the house and doubled back. Our total length of buried tubing is in the 230 feet range.  

Back Fill

Once the tubing is laid we can begin to push the soil back against the house. 

With the back fill done, you can see we need more dirt...

The Pond

We dug a pond to give us some "free" fill.

The overall pond is roughly 5000 square feet. We made it to 7 feet deep before we hit a natural spring.

We did find some really nice damp clay under the top soil. So this is what we used to distribute around the rest of the house.

Photo looking at the front of the house

Photo looking at the south end of the house

Photo looking at the back of the house

Photo looking at the north side of the house (Breezeway and garage side). 

We had to wait on the foundations for those for truck access to the raised fill septic system.

The tube you see sticking out of the ground is our sump pump. (The tubing sticking out is the temporary discharge line)

Exterior Sump Pump

I am not sure of you picked up on this at all from previous posts, but we will be incorporating an exterior sump pump to our house. This is very uncommon in new construction, but can be used in retrofit situations to keep basements dry. We did this for a few reasons.

1. A sump pump pumps water out from around the foundation drains. These drain pipes are corrugated plastic pipes with small slits in them to allow water into them. When they are not filled with water they are excellent paths for radon in basements. the gasses can easily get into the pipes and into the sump crock in the house. We are building in a higher risk area of radon, and wanted to ensure we would be radon free. 
2. A sump pump would be penetrating the sub slab insulation creating a pretty substantial "Thermal Bridge". There is no good way to insulate around a sump crock.
3. We eliminate a penetration in the foundation wall where the pump would pump the water out into the yard.

Our exterior sump pump will discharge into our pond. We did make sure the building official and the pond engineer were OK with this situation before we decided to do it. The pump will be installed on a lanyard so it can be easily changed out in the event it fails and there will be an indicator light on a float switch in the even the sump pump either fails or cannot keep up with the incoming water.

We will be framing the deck soon and getting started on the septic system!  

Whole House Ventilation

Whole House Ventilation

I think the biggest question / complaint I hear from builders today is - Why do I need to make a house this tight, then add a fan to bring in fresh air? If I made it leakier I could save the homeowner some money.

While to a certain extent they are right. They can sell you a less expensive, leakier house that is missing any kind of forced ventilation for the house. After all, your parents house never needed ventilation, their parents never needed ventilation, why do we need it?

The fact is, for our climate in Rochester, NY, it is more efficient in the winter to run a 45 watt machine that recovers 90% of the heat, than to heat up all of the 10 degree air leaking into the house with your furnace, plus your furnace fan.

The air leaking into your house is much drier (lower relative humidity) than the air inside your house. This means you either increase the thermostat temperature or add humidity to the air with a humidifier. Also in order for air to be coming into the house, some of the air inside the house must be leaving. So where does it go?

Green Building Advisor has some GREAT visuals of why infiltration and exfiltration is bad

The exfiltration of the indoor air with its high relative humidity cools and condenses inside the wall. This can lead to extensive moisture within your wall and in extreme cases, extensive wall rot as seen above. This moisture problem can be masked by common building materials like Tyvek, and Vinyl Siding since they will not show any problems until it is too late (with wood siding moisture in the wall is be evidenced by peeling paint or breakdown of the wood siding).

Passive House takes the Building Science theme "Build it Tight and Ventilate it right" to a whole new level.

The pictorial  from the CDC below illustrates some common concerns with building a tight home. Proper ventilation is essential to prevent compounding of these issues which can result from tight building practices. . Reducing the amount of infiltration / exfiltration is also healthier for the building.

 

You cannot rely on a leaky, non ventilated house to ventilate itself via infiltration/exfiltration, exhaust fans (bathroom, range hood). Bringing in fresh air is just as important as exhausting stale air. Opening windows is a great ventilation solution, but these sources for poor indoor air quality (above) still exist in the winter (and summer when you are air conditioning) when you have the windows closed.

The bath fans and range hoods in a standard house provide spot ventilation by mechanically exhausting air. The fresh air is then drawn into the house through a different 'path of least resistance'. A passive house, however, is equipped with an air tight structure and a whole house ventilation system.

In a passive house, usually the best indicator of indoor air quality is carbon dioxide concentration.  In our area outdoor carbon dioxide levels are in the 400-500 parts per million (ppm). The whole house ventilation system is designed to keep the indoor air at outdoor levels. Some of the most common sources of carbon dioxide in a home are:

• Respiration (A typical human breath contains about 100 times the outdoor levels)
• Cooking with gas (by product of combustion - along with water vapor)
• Unvented Gas Furnaces (THESE ARE NEVER A GOOD IDEA!)

This is a graph from a 2012 publish paper that was assessing CO2 levels and inhabitants decision making

As you can see, in an office setting it only take 50 minutes before CO2 levels can rise to a level leading to poor performance.

To keep CO2 levels reduced in a passive house we always focus on the sources first. So it is easiest to no have any combustion appliances in a passive house (That includes, fire places, gas stove, gas dryers, furnaces, gas water heaters, etc) - it doesn't mean you can't have them, it just means it is much better if you don't. Then all we are worried about is the CO2 from respiration.

Ventilation System Design

This is where the design of the ventilation system comes in.

We want to supply fresh air to bedrooms and living spaces.
We want to remove odorous and stale air from bathrooms and kitchens (and laundry too).

We keep the supply and extract registers within the house separated to allow proper penetration of fresh air throughout the home. If the fresh air is being supplied into the bedroom, the extract register in the bathroom will draw that fresh air through the house toward bathroom where it will be extracted. If the registers are too close together the fresh air will not be as efficiently distributed.


See our proposed ventilation system design from Zehnder America

The blue dots indicate supply air. The red dots indicate the extract air. We will be supplying air to all of the bedrooms, and the office and we will be extracting air from all of the bathrooms, laundry room and the kitchen (the placement of the extract in the kitchen is intentional, this will allow efficient extraction of the cooking smells while limiting grease buildup on the register by avoiding close proximity to the range). We will run a charcoal recirculating hood above the range to remove the cooking grease.

The Zehnder America System will be supplying about 120 CFM continuously of fresh filtered air. In contrast the standard furnace fan runs at about 1200 CFM, and is just recirculating the air already inside your house, not supplying fresh outdoor air. The air flow for the Zehnder System is so low, you will not feel the air moving through the registers.

See this video for more details on the Zehnder Comfosystem

I should mention that the earth tube idea mentioned in the video is not really a good idea in our area due to the much wider temperature range and higher humidity levels than in Central Europe (where Zehnder system was designed for). There is another option that we will be using from Zehnder. It is called Comfofond. It is actually a small geothermal loop installed around the footer of the house. The loop is filled with brine and flows though a heat exchanger to temper the incoming air in the summer and winter. For example, in the winter the 5 degree outdoor air will be raised to about 40 degrees using the heat in the ground which is delivered by this brine loop, this will make the ventilation heat recovery more efficient.

I should clarify that this geothermal system is not a heat pump like those systems you commonly see advertised or installed in our area, it does not require wells or loop field or any extra excavation to install. No refrigerant is needed. It is not designed to heat or cool the house, it is only designed to temper the incoming air to make the ventilation system more efficient. There is also a significant cost difference when using the Comfofond system as compared to a full geothermal heat pump system for whole house heating. Geothermal heat pump systems also do not provide ventilation as the Zehnder system does.

So this diagram shows how the heat exchanger works

The Comfofond system is installed directly in front of the 'fresh air in' to ensure maximum efficiency.

The Zehnder system is up to 90% efficient and when combined with the Comfofond you can be extracting 68 degree air from the home and supplying fresh outdoor air at 66 degrees when it is only 5 degrees outside!

So now a single air source heat pump inside the house will only have to heat the incoming air 2 degrees to maintain the temperature in the home. In a standard house, with leaky walls, your furnace is trying to heat the incoming 5 degree air back up to a comfortable temperature and meanwhile your heated air continues to escape through the walls-incredibly inefficient!

In the next post we will talk more about how the air source heat pumps improve efficiency over a standard build.